Author Archives:

On Molecular Genetics and the Origin of the Polar Bear.

by noahmattoon

Polar bear

Understanding the history of species is critical to understanding evolutionary processes and for making predictions about how biodiversity will fare in a rapidly changing climate. Information about how species are related (phylogeny) and how their populations have responded to past climate change (historical demography) can inform us about the conditions under which they have evolved and adapted, and how they might respond to changes currently under way.

Modern scientists get at these questions by examining two types of data: the fossil record and patterns of DNA sequence variation. The fossil record is relatively straightforward. You find a fossil in location X. You identify it as species Y and you use some method to (e.g. radiocarbon dating) to infer it was there at time Z. Making inferences from DNA sequence variation, by contrast, involves complex, computer-intensive statistical analyses, and the field is in a state of tumultuous, rapid advance.

A fascinating case study that involves the integration of fossils and DNA sequence data, and illustrates the ways in which rapid statistical advances are changing our understanding of species’ evolutionary histories is that of the origin of the polar bear (Ursus maritimus).

Continue reading →

A post about inbreeding depression in which I make no reference to the movie “Deliverance.”

by noahmattoon
Bighorn sheep (Ovis canadensis) at Glacier National Park in Montana. Photo by Noah Reid.

As humanity spreads out over the globe, finding ever more clever ways to domesticate wild landscapes and harness natural processes to its will, many species of wildlife find their natural distributions becoming fragmented.  Iconic North American species such as grizzly bears, red-cockaded woodpeckers, and the American burying beetle today inhabit only small fractions of the ranges they occupied only 100 years ago. A result of this fragmentation is that many individuals exist in small, isolated populations.  In these populations, a curious phenomenon often emerges, one that can only be understood in light of some basic evolutionary theory.  That phenomenon is known as inbreeding depression, and it refers to the decline in average fitness of individuals in a shrinking population.

Inbreeding depression is essentially a result of individuals in small, isolated populations being more likely to mate with close relatives.  It’s well known that mating with close relatives produces less fit offspring, and the aggregate effect in natural populations is seen as low average fitness and an ensuing low population growth rate.  This can be a serious problem in populations subject to conservation efforts because even after protective measures have been taken (removing threats, restoring habitat) recovery can be hindered by inbreeding depression.  Inbreeding depression is slightly more complicated than this, however, because it is not consistently seen in all small populations.  In some island populations with very small population sizes (such as the Chatham Robin, Petroica traversi) inbreeding depression has not been observed (Jamieson et al. 2006).

Continue reading →

Mass extinction: Did ancient humans get the party started 30,000 years ago?

by noahmattoon
Image

Bison priscus. The now-extinct Steppe Bison. This mummified individual, known as Blue Babe, was found in Fairbanks, AK, by a gold miner and is approximately 36,000 years old. Credit to Travis S.

During the last ice age, huge numbers of large mammals roamed the temperate zones of North America and Eurasia that lay south of vast continental glaciers. Familiar animals such as Woolly Mammoths, Woolly Rhinoceroses, Reindeer, Musk Oxen, Steppe Bison and the wild ancestors of domesticated horses along with more exotic creatures such as Glyptodon, a car-sized relative of armadillos and Megatherium, an enormous ground-dwelling sloth were abundant. With the ending of the ice age, which began around 21,000 years ago, many of these species experienced dramatic declines or went extinct. Woolly Rhinos, Mammoths, Glyptodon, and Megatherium went completely extinct, while Bison, Reindeer, Musk Oxen and wild Horse went through serious declines and range contractions.

These population declines roughly coincided with another major event in earth’s history, the global expansion of modern humans. Because of this synchronicity, there has long been debate about whether either is the cause. Did humans fuel their global expansion by hunting these animals to extinction, were they victims of a changing climate, or was it some combination of the two?

To answer this question, we need to know two main things. First, did climate change create extremely inhospitable environments for these species? Second, did the decline of these species coincide with contact with humans?

Continue reading →

A post on one of biology’s most confounding riddles: the latitudinal gradient in biodiversity.

by noahmattoon

A beautiful, but comparatively species poor forest in eastern Oregon

Explaining global patterns of biodiversity is a fundamental goal in biology. Understanding how the tens of millions of species on earth have arranged themselves into populations, communities, and ecosystems, is critical for conserving them in the face of a rapidly growing human population and global climate change.

ResearchBlogging.orgThe latitudinal gradient in species diversity is perhaps the most famous such pattern, and it has confounded biologists for decades. Almost invariably across taxonomic groups, hemispheres and continents, as one moves from polar regions towards the equator, species diversity increases (see the figure for a depiction of global bird diversity). The concept of diversity here can be broken down into three parts: “alpha diversity” or the diversity of species in a single location; “beta diversity”, or the turnover of species observed when moving among locations; and “gamma diversity” or the diversity of species found in an entire region. The latitudinal diversity gradient holds true for all three elements.
Continue reading →

Science-y picture of the *random time interval*!

by noahmattoon

“We will call phoresy all phenomena of transport in the strict sense, that is, those cases in which the transport host serves its passenger only as a vehicle”

-Pierre Lesne (1896)

This is a photo of a crane fly (Tipulidae) with three pseudoscorpions (a type of Arachnid) holding on to its thorax.  This has been observed frequently, and it is thought that the pseudoscorpions are merely attempting to hitch a ride, a behavior known as phoresy.  Where they are hoping to go is beyond me, but the fly was overburdened and flying erratically, so they probably didn’t make it far.  The photo was taken in Clark Creek Natural Area, Mississippi.